In nuclear reactors the fuel elements are generally arranged in the form of assemblies which may be withdrawn individually in order to be placed in a deactivation pool.
Each assembly consists of a plurality of elements called pencils which are arranged vertically in a supporting frame. The frame consists of two endpieces called the upper tubeplate and lower tubeplate to which are attached the ends of a plurality of vertical tubes which substitute certain pencils. The tubes serve, for example, for the guidance of control bars. Between the upper and lower tubeplates are arranged a number of bracer grids which bear against the tubes and which are equipped with members for retaining the fuel elements.
Each endpiece comprises a plane base in which are arranged two series of orifices. The ends of the tubes are engaged and fixed into the orifices of the first series, whereas the second series serves for the flow of cooling fluid between the fuel elements.
The lower endpiece bears against the lower internal fittings. The latter are bounded by the lower plate of the core which is equipped with dowels for centreing which engage in orifices arranged in four feet placed at the corners of the lower endpiece.
Similarly the upper endpiece is likewise equipped at its corners with orifices in which engage dowels for centreing which are integral with the upper plate of the core, which bounds the upper internal fittings.
Periodically it is necessary to proceed with recharging with fuel. For this purpose the upper internal fittings are removed in order to gain access to the whole of the fuel assemblies. Each assembly may be withdrawn as a unit and placed in a cell in a deactivation pool. In this pool a remote-controlled machine proceeds with dismantling of the fuel assembly. That is, it is necessary to be able to gain access to the pencils in order to change or eliminate certain of them which are recognised as defective or able to be recycled.
Similarly the ability for dismantling enables re-use of the pieces of the skeleton and in parallel more compact storage of the pencils withdrawn from the skeleton.